Derivative Financial Instruments (Potential Loss on Counterparty Exposures) (Details) $ in Millions	Sep. 30, 2018 USD ($)
Derivative [Line Items]
Derivative Potential Loss	$ 32
Union Electric Company
Derivative [Line Items]
Derivative Potential Loss	31
Ameren Illinois Company
Derivative [Line Items]
Derivative Potential Loss	$ 1

Potential loss on counterparty exposures related to derivative instruments, including NPNS contracts, after consideration of all collateral held and application of master trading and netting agreements.

No definition available.

Name:	aee_DerivativePotentialLoss
Namespace Prefix:	aee_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant